There is a great emphasis on high productivity in the photosensitive materials market. Photofinishers that use photosensitive paper to produce color prints desire short processing times in order to increase output. One way to obtain rapid processing is to accelerate the development time by increasing the chloride content of the emulsions; the higher the chloride content the higher the development rate. However, it is also known that the higher the chloride content is, the harder it is to obtain high, invariant photosensitivity. Emulsions that are primarily silver chloride are more difficult to spectrally sensitize than emulsions used previously such as silver bromide or chlorobromide emulsions because the conduction band of silver chloride is higher than that of silver bromide (C. R. Berry, Photo. Sci. & Eng. 19, 93, (1975)).
The problem with sensitizing efficiency is especially true in the red-sensitive layer of many color print photosensitive materials and is related to the red sensitizers reduction potential. Correlations between dye reduction potentials and sensitizing efficiency on high silver chloride emulsions are discussed by W. Vanassche, J. Photo. Sci., 21, 180 (1973) and P. B. Gilman, Jr., Photo. Sci. & Eng. 18, 475 (1974). Another common problem with the red sensitive layer of color print paper which contains an emulsion that is primarily silver chloride, is an undesirable sensitivity to temperature. An increase in temperature of the paper during exposure results in an increase in red speed of the red sensitive layer making it difficult for the photofinisher to adjust his printing conditions. This results in a loss in operating efficiency.
An example of heat sensitivity is illustrated below. Material C has no propensity for heat sensitivity while Material A and B have equal propensity but in opposite directions. Color photographic materials typically respond to three regions of the spectrum, red, green and blue with different emulsions and, as an example for color positive paper such as EKTACOLOR Paper, will produce cyan, magenta and yellow dye images when processed in Process RA-4. If the paper temperature changes during the day as it is printed such as due to changing ambient conditions or warming up in the printing environment, the prints can change in density causing a variability in the image produced. With color products a mis-match in the heat sensitivity response of the three layers results in a color shift in the prints. So, while it would be useful to have low heat sensitivity to preserve color consistency in printing, it is more important with color products to have a consistent heat sensitivity shift in all three layers to avoid a shift in the more critical area of color balance. Almost all of the materials used to prepare silver halide emulsions can under some conditions affect the heat sensitivity of the resulting photographic materials. It is therefore desirable to have the ability to adjust the heat sensitivity of a particular emulsion to the appropriate level to match the other two layers.
______________________________________ Speed (Log E) of Speed (Log E) of Heat Sensitivity Materials at 22.degree. C. Materials at 40.degree. C. (Delta Log E) ______________________________________ Material A 1.90 2.00 +.10 Material B 2.00 1.90 -.10 Material C 1.90 1.90 0.00 ______________________________________
European published patent application EP 605,917 A2 describes red dyes that give high speed and reduced heat sensitivity when used on high chloride emulsions. However, by the use of these red sensitizers, the heat sensitivity of the cyan layer is so low that it no longer matches that of the magenta and yellow records. This causes an undesirable color balance shift during thermal changes. It is therefore desirable to provide a means of adjusting the heat sensitivity in the cyan layer so as to match that of the magenta and yellow layers. It is toward this end that this invention is directed.